It is known that organic and polymeric materials with large delocalized .pi.--electron systems can exhibit nonlinear optical response, which in many cases is a much larger response than by inorganic substrates.
In addition, the properties of organic and polymeric materials can be varied to optimize other desirable properties, such as mechanical and thermoxidative stability and high laser damage threshold, with preservation of electronic interactions responsible for nonlinear optical effects.
For materials having second-order nonlinear optical response, it can be shown by theoretical considerations that a noncentrosymmetric macrostructure is required. Typically, the same is achieved by heating a thermoplastic polymer containing NLO active chromophores above its glass transition temperature and subjecting it to an electric field, then cooling it with the field still on so that the ordered structure is frozen into place. It has been found that a structure so produced can be stabilized over time by control of heating and cooling during this "poling" process by way of heat or pressure treatments.